Maybe you're the one who can write a check, but this is a difficult topic...
I do corporate accounting for baroque software and I can write an invoice and pushing people to pay for it is still quite a sales challenge - you need to be able to talk to high enough people and prove the value of what you're offering on top of the software you are already giving for free. It's not different to a standard issue sales exercise, except a little harder. This is not a skill that most open source project maintainers would consider themselves experts at.
Giving advice like that is very dangerous - "only if you did that, you would make money". It's not a given that it would lead to something more than couple hundred dollars.
I suspect that is never going to change, and the same is true for many services.
There is a community site I frequent that keeps itself afloat with a freemium model (if you pay you get more features; but you still get 98% of features even as a free user; there are no ads on that site). Many people understand this and pay to keep the site running, but something like 10%-20% of users claim that it's just a money grab because "facebook offers essentially the same features and they can do it for free, so obviously this site is trying to make a profit on our back".
There is expectation that because some software is free, most software is free. Similarly, there's an expectation that if some websites are free, most similar websites should be free as well.
p.s.: the main cost to using Facebook in my opinion is privacy, and I value my privacy much more than what I get from Facebook. Obviously. other people value privacy and facebookness differently.
I do corporate accounting for baroque software and I can write an invoice and pushing people to pay for it is still quite a sales challenge - you need to be able to talk to high enough people and prove the value of what you're offering on top of the software you are already giving for free. It's not different to a standard issue sales exercise, except a little harder. This is not a skill that most open source project maintainers would consider themselves experts at.
Giving advice like that is very dangerous - "only if you did that, you would make money". It's not a given that it would lead to something more than couple hundred dollars.